The present invention relates to the field of gas generation and, more particularly, to an apparatus for controlling the generation of gas from a liquid/solid reaction or the like.
Recent environmental concerns have led to increased focus on developing clean energy production methods to reduce the dependence on oil and to reduce the emission of hydrocarbons thought to be harmful to the environment. One such clean energy source is hydrogen. The main byproduct of hydrogen combustion is water. Generation of fuel grade hydrogen can involve the reaction of an alkali metal or a metal hydride that will react with water to form hydrogen gas. If this reaction is not controlled, the reaction could result in an over-pressurization situation which would be very dangerous.
When generating hydrogen gas from the oxidation of highly reactive metals, it is important to regulate the production rate of the gas. A variable-flow valve can regulate the flow rate at which the gas is delivered for an intended application, but the variable-flow valve without another control mechanism does not regulate the rate at which gas is generated. The maximum flow rate will be dependent on the pressure generated and maintained by the reaction. A separate control mechanism is necessary to manipulate the rate and pressure at which gas is generated. The prior art describes a variety of ways to manipulate a reaction which generates gas.
U.S. Pat. No. 5,728,464 to Checketts discloses a method in which pellets of sodium or other reactive alkaline metals are encapsulated in a thin layer of plastic or aluminum. These pellets float in a pressure tank of water. The tank contains an apparatus to fetch one pellet and to cut the plastic coating or remove the aluminum coating via electrolysis, thus allowing the metal to react with the water and generate hydrogen gas. Pressure sensors stop the pellet cutter or pellet electrolysis apparatus when the high pressure limit is reached, thus stopping gas generation. As the pressure drops to a lower limit due to the consumption of the previously produced hydrogen, the apparatus to remove the protective coating from the reactive pellet is activated. As the pellet is exposed to the liquid reactant the production of hydrogen begins again. This system requires finely tuned pressure sensors and involves complex mechanics.
Various methods exist for metering a liquid, as needed, into a tank of solid reactant mixture or vice versa and controlling the process by monitoring tank pressure. Such methods can have hysteresis issues, especially if the reaction is slow to start. The control system may sense a low gas pressure and add too much of the metered reactant. As a result, the reaction heats up, accelerates, and generates too much gas leading to an over-pressure condition. One example of such a method, disclosed in U.S. Pat. No. 7,144,567 to Andersen et al., involves metering flakes of solid reactant through a hand cranked rotary airlock into a pressurized reaction vessel.
U.S. Pat. No. 5,867,978 to Klanchar et al. discloses metering of a reactant fluid into a reaction pressure vessel. The solid reactants are limited to very high reaction rate substances like lithium, and lithium hydride. The solid reactant is often heated to molten temperatures to provide near instantaneous reaction speeds requiring very complex controls.
U.S. Patent Application Publication No. US2004/0205997A1, published Oct. 21, 2004, in the name of Youngblood, discloses a vertical reactor of two compartments connected by a pipe and valve. Solid reactants are loaded into the lower compartment, with the fluid loaded into the upper compartment. When the valve is opened, the liquid components gravity feed into the lower compartment and the reaction begins. As pressure builds in the lower compartment, the liquid is forced back into the upper compartment, thus uncovering the solid reactants and stopping the reaction.
Eborall et al. discloses in U.S. Pat. No. 2,623,812 that solid reactants may be suspended in an open-bottom cylinder that is immersed in a larger tank of water, and, as the pressure rises due to gas generation, the water level in the cylinder is forced lower, eventually uncovering the solid reactants and stopping the reaction. Eborall et al. only provides for delivery of hydrogen at near atmospheric pressure.
U.S. Pat. No. 3,554,707 to Holmes et al. discloses a gas generator having a bellows to raise or lower the level of water in response to pressure inside the generator. As the gas pressure builds, the bellows expands in response to the increase in pressure and the water level drops. The contact between a fuel cartridge and the water is lost and the reaction is terminated. An enclosure for the bellows has multiple holes in an end wall and a catch to hold the bellows in an expanded position. U.S. Pat. No. 6,800,258 to Andersen et al. shows another bellows system.
The known methods of controlling gas generation involve either overly complex or fragile or expensive mechanisms. Therefore, a need remains for improvements in control systems for on-demand gas generators.